Spouses rely on one another for practical and emotional support. Couples also age together, and co- experience health, sickness, and disability. The risk of disability and disease increases with age in part because adaptation to and recovery from life stressors depletes biological reserves, resulting in cumulative biological risk. Spouses have been found to resemble one another in their health, health behaviors, and well-being, and this resemblance signals homogeneity in resources within couples that could replicate or even amplify health inequalities. Although spousal resemblance in health and health behaviors is well- documented, little is known about the extent to which biomarkers of multisystem strain on biological resources, known to cumulate within individuals, also cluster within couples to form indicators of couple's cumulative risk. Similarly, patterns of change in estimates of couple's cumulative risk are unknown. Finally, the added predictive value of couple's cumulative risk on health is not yet determined. Our central hypothesis is that accounting for couple's cumulative risk will improve characterizations of an individual's current and future health. To this end, our project will: (Aim 1) Establish couple's cumulative risk as an indicator of multisystem biological risk by a) estimating the extent of couple's cumulative risk in a population sample of married couples in older adulthood; b) showing couple's shared experiences to contribute to couple's cumulative risk over and above other couple similarities; and c) demonstrating that, similar to indices of individual's cumulative risk, couple's cumulative risk is more prevalent in disadvantaged populations; (Aim 2) Distinguish patterns of stability and change in couple's cumulative risk by a) identifying patterns of stability, convergence, and divergence over time; and b) replicating patterns of couple's cumulative risk in an independent sample; and (Aim 3) Identify the predictive potential of couple's cumulative risk on health outcomes through a) applying couple's cumulative risk to predict future health; and b) evaluating the best method to estimate couple's cumulative risk. We will accomplish our aims by analyzing biological, health, sociodemographic, and relationship data from the 2008 through 2014 waves of the Health and Retirement Study (n = 3,284; 1,642 couples), a nationally representative panel study of Americans age 51 and older (MAge = 68.26, SD = 8.94). Known biomarkers of multisystem biological risk will be used to estimate univariate (single-item spousal resemblance), index (couple-level index of established cumulative biological risk index), and multivariate (latent couple-level shared variance in multiple indicators of cumulative risk) representations of couple's cumulative risk. Data will be analyzed using analytic strategies appropriate for longitudinal dyadic data. Together, this project will establish couple health as an essential component of individual health, and provide the evidence and tools necessary to further push research, policy, and practice to understand individual health within the context of relationships with others.